Defect detection system

ABSTRACT

Scattered radiation from a sample surface is collected by means of a collector that collects radiation substantially symmetrically about a line normal to the surface. The collected radiation is directed to channels at different azimuthal angles so that information related to relative azimuthal positions of the collected scattered radiation about the line is preserved. The collected radiation is converted into respective signals representative of radiation scattered at different azimuthal angles about the line. The presence and/or characteristics of anomalies are determined from the signals. Alternatively, the radiation collected by the collector may be filtered by means of a spatial filter having an annular gap of an angle related to the angular separation of expected pattern scattering. Signals obtained from the narrow and wide collection channels may be compared to distinguish between micro-scratches and particles. Forward scattered radiation may be collected from other radiation and compared to distinguish between micro-scratches and particles. Intensity of scattering is measured when the surface is illuminated sequentially by S- and P-polarized radiation and compared to distinguish between micro-scratches and particles. Representative films may be measured using profilometers or scanning probe microscopes to determine their roughness and by the above-described instruments to determine haze in order to build a database. Surface roughness of unknown films may then be determined by measuring haze values and from the database.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is related to U.S. patent application Ser. No.08/770,491, filed Dec. 20, 1996, U.S. Pat. No. 6,201,601, issued Mar.13, 2001 and the application being filed concurrently herewith. Therelated applications and the issued patent are incorporated herein byreference in their entireties.

BACKGROUND OF THE INVENTION

[0002] This invention relates in general to defect detection, and, inparticular, to an improved system for detecting anomalies on surfaces,such as particles and surface-originated defects such ascrystal-originated particles (“COPs”), surface roughness andmicro-scratches.

[0003] The SP1^(TBI)™ detection system available from KLA-TencorCorporation of San Jose, Calif., the Assignee of the presentapplication, is particularly useful for detecting defects on unpatternedsemiconductor wafers. While the SP1^(TBI) system provides unsurpasseddefect sensitivity on bare wafers or unpatterned wafers, this is not thecase when it is used for inspecting wafers with patterns thereon such aswafers with memory arrays. In this system, all of the radiationcollected by a lens or ellipsoidal mirror is directed to a detector toprovide a single output. Thus, since pattern on the wafer will generateFourier and/or other strong scattering signals, when these signals arecollected and sent to the detector, the single detector output becomessaturated and unable to provide information useful for detecting defectson the wafer.

[0004] Conventional techniques for detecting defects on wafers areeither tailored for the inspection of patterned wafers, or forinspecting unpatterned or bare wafers, but not both. While inspectionsystems for detecting patterned wafers may be also used for inspectingunpatterned wafers, such systems are typically not optimized for suchpurposes. Systems designed for the inspection of unpatterned or barewafers, on the other hand, may have difficulties handling thediffraction or other scattering caused by the patterned structures onpatterned wafers, for reasons such as those explained above.

[0005] For the inspection of patterned wafers, entirely differentinspection systems have been employed. One commercial system, known asAIT™ inspection system, is available from the Assignee of the presentapplication, KLA-Tencor Corporation of San Jose, Calif.; such system isalso described in a number of patents, including U.S. Pat. No.5,864,394. In the AIT system, spatial filters are employed to shield thedetectors from the diffraction or scattering from the patternedstructures on the wafer. The design of such spatial filters can be basedon prior knowledge of the patterned structures and can be quite complex.Furthermore, this system utilized a die to die comparison process inorder better to identify the presence of a defect.

[0006] None of the above-described instruments is entirely satisfactoryfor the inspection of patterned wafers. It is therefore desirable toprovide an improved defect detection system for patterned wafers inwhich the above difficulties are alleviated. To further economize on thespace required for inline inspection, it is desirable to provide aninstrument that can be optimized for both unpatterned and patternedwafer inspection.

[0007] Chemical mechanical planarization (CMP) has gained wideacceptance in the semiconductor industry. The CMP process, however, alsocreates many types of defects that can significantly impact the yield ofan integrated circuit (IC) device if the defects are not properlycontrolled. Among the CMP defects, the micro-scratch has a strong impacton IC yield. Therefore, it is desirable to be able to detect anddifferentiate micro-scratches and other CMP defects from particles.

[0008] One important parameter for monitoring the quality of unpatternedor bare films on silicon wafers is the surface roughness. Surfaceroughness is typically measured by an instrument such as the HRP®instruments from KLA-Tencor Corporation, the Assignee of the presentapplication, or by means of other instruments such as atomic forcemicroscopes or other types of scanning probe microscopes such asscanning tunneling microscopes. One disadvantage of such instruments isthe slow speed of their operation. It is therefore desirable to providean alternative system which may be used for giving a measure of surfaceroughness at a speed much faster than the above-described instruments.

SUMMARY OF THE INVENTION

[0009] One aspect of the invention is based on the observation that thecollectors in the SP1^(TBI) instruments preserve the azimuthalinformation of the scattered radiation by the surface inspected. Thus,by segmenting and directing the scattered radiation collected by thetype of collectors used in the SP1^(TBI) instruments at differentazimuthal positions to separate collection channels, the above-describeddifficulties are overcome so that an instrument may be constructed whichis also optimized for the detection of patterned wafers. In this manner,a compact instrument can be achieved for measuring defects of patternedwafers. In addition to the ellipsoidal mirror used in the SP1^(TBI)instruments, other azimuthally symmetric collectors may be used, such asa paraboloidal mirror used together with one or more lenses.

[0010] As in the SP1^(TBI) system, the surface inspection system of oneaspect of this invention collects radiation scattered from the surfaceby means of a collector that collects scattered radiation substantiallysymmetrically about a line normal to the surface. By directing todifferent channels the collected radiation scattered at differentazimuthal angles about the line or another direction, these channelswill carry information related to scattered radiation at correspondingrelative azimuthal positions of the scattered radiation. Preferably, thechannels are separated from each other by separators to reducecross-talk. The collected scattered radiation carried by at least someof the channels may then be used for determining the presence and/orcharacteristics of anomalies in or on the surface. In addition, themultiple views of the same event can significantly facilitate theprocess of real time defect classification (RTDC).

[0011] In the above-described scheme, if only a portion of the collectedradiation is directed to the different channels, while another portionof the collected radiation at different azimuthal angles are directed toa single detector for providing a single output as in the conventionalSP1^(TBI) scheme, the system can then be used for inspecting bothunpatterned and patterned wafers. In other words, if the SP1^(TBI)scheme is modified by diverting a portion of the collected radiation inthe manner described above to different channels while preservingazimuthal information, a versatile tool results that can be optimizedfor the inspection of both unpatterned and patterned wafers. In thismanner, semiconductor manufacturers no longer have to employ twodifferent tools, each optimized for the detection of patterned orunpatterned wafers.

[0012] In the above-described scheme, since collected radiation atdifferent azimuthal angles about the line normal to the surface aredirected to different collection channels and converted into separatesignals, the signals containing pattern diffraction can be discarded andthe remaining signals not containing pattern scatter may then be usedfor the detection and classification of anomalies in or on the surfaceof the wafer. While the above-described systems are particularly usefulfor the inspection of semiconductor wafers, they can also be used for heinspection of anomalies on other surfaces such as flat panel displays,magnetic heads, magnetic and optical storage media and otherapplications.

[0013] Another aspect of the invention is based on the observation thatthe radiation collected by a collector (such as the one described above)may be filtered by means of a spatial filter having an angular gap of anangle related to the angular separation of expected radiation componentsscattered by pattern on the surface. In this manner, the filteredradiation at some relative positions of the surface relative to thefilter will contain information concerning defects of surfaces unmaskedby pattern scattering that would interfere with the measurements. Whensuch radiation is detected by the detectors, the detector outputs canthen be used for detecting the presence and/or characteristics ofanomalies in or on the surface.

[0014] The SP1^(TBI) tool or the above-described systems may be used fordistinguishing between particles and micro-scratches caused by CMP.Scattered radiation along directions close to the normal direction iscollected by a first detector and radiation scattered along directionsaway from the normal direction is collected by a second detector. Aratio is then derived from the outputs of the two detectors to determinewhether an anomaly on the surface is a micro-scratch or a particle.

[0015] The CMP micro-scratches tend to scatter radiation from an obliqueincident beam in the forward direction while particles tend to scattersuch radiation more evenly. Radiation scattered by the surface alongforward scattering directions is collected separately from scatteredradiation in other scattering directions. Two different signals arederived from the separately collected scattered radiation and comparedfor determining whether an anomaly on the surface is a micro-scratch orparticle.

[0016] In another aspect of the invention, an S-polarized radiation beamand a P-polarized radiation beam are provided sequentially in obliquedirection(s) to the surface during two different scans of the surface.The radiation scattered by a defect during the first and second scans iscollected to provide a pair of signals indicative of the scatteredradiation of two different incident polarizations. The pair of signalsis then compared to a reference to determine whether an anomaly on thesurface is a micro-scratch or particle.

[0017] In order to speed up the process for determining the surfaceroughness of thin films, a database correlating haze values with surfaceroughness of thin films is provided. The haze value of the surface isthen measured by a tool such as the SP1^(TBI) or one of theabove-described systems, and a roughness value of the surface may thenbe determined from the measured haze value and the database. Forexample, the database may be compiled by means of a tool such as theSP1^(TBI) or one of the above-described systems for measuring the hazevalues of representative thin films and another tool such as an HRP®profiler or other type of profilometer or a scanning probe microscopefor measuring the surface roughness of such films.

[0018] Any one of the above-described aspects of the invention may beused individually or in any combination to achieve the advantagesdescribed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a schematic diagram of the SP1^(TBI) system useful forillustrating the invention.

[0020]FIG. 2 is a schematic diagram illustrating a convergent hollowcone of radiation to illustrate one aspect of the invention.

[0021]FIG. 3A is a schematic view of a possible arrangement of multiplefiber channels for carrying scattered radiation collected by theellipsoidal collector of the system of FIG. 1 to illustrate one aspectof the invention.

[0022]FIG. 3B is a schematic view of an multi-anode photomultiplier tube(PMT) that can be used in conjunction with an arrangement of multiplefiber channels such as that shown in FIG. 3A to illustrate one aspect ofthe invention.

[0023]FIG. 4 is a schematic view of an arrangement of fiberchannels/multiple detectors for carrying scattered radiation collectedby the lens collector in the narrow channel of the system of FIG. 1 toillustrate an aspect of the invention.

[0024]FIG. 5A is a cross-sectional view of a defect inspection system toillustrate the preferred embodiment of the invention.

[0025]FIG. 5B is a cross-sectional view of an arrangement of separateoptical channels used in the embodiment of FIG. 5A.

[0026]FIG. 6A is a cross-sectional view of a defect inspection system toillustrate an alternative embodiment of the invention.

[0027]FIG. 6B is a cross-sectional view of an arrangement of segmentedoptical channels used in the embodiment of FIG. 6A.

[0028]FIG. 7 is a top view of a portion of a defect inspection system toillustrate another alternative embodiment of the invention.

[0029]FIG. 8A is a schematic view of a multi-element detector in theembodiment of FIG. 7.

[0030]FIG. 8B is a schematic view of two multi-element detectors for usein the embodiment of FIG. 7.

[0031]FIG. 9A is a partly cross-sectional and partly schematic view of adefect inspection system to illustrate yet another alternativeembodiment of the invention.

[0032]FIGS. 9B and 9C are schematic views of filter wheels useful in theembodiment of FIG. 9A.

[0033]FIG. 10 is a schematic view of a two-dimensional diffractioncomponents from a pattern on a surface to be inspected illustrating anaspect of the invention.

[0034]FIG. 11 is a schematic view of a defect inspection system toillustrate one more alternative embodiment of the invention.

[0035]FIG. 12 is a schematic view of an asymmetric mask for use in thedifferent embodiments of this invention.

[0036]FIGS. 13A and 13B are schematic views of two masks used with thedifferent systems of this application to illustrate yet another aspectof the invention.

[0037]FIG. 14 is a graphical plot of the interference intensity of thinfilm surfaces when illuminated with radiation of three differentpolarizations to illustrate another aspect of the invention.

[0038]FIG. 15 is a graphical plot of haze and surface roughness toillustrate yet another aspect of the invention.

[0039]FIG. 16 is a block diagram illustrating a system measuring surfaceroughness and haze of representative films for compiling a databaseuseful for the invention of FIG. 15. For simplicity in description,identical components are identified by the same numerals in thisapplication.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040]FIG. 1 is a schematic view of the SP1^(TBI) system 10 availablefrom KLA-Tencor Corporation of San Jose, Calif., the assignee of thepresent application. Aspects of the SP1^(TBI) system 10 are described inU.S. patent application Ser. No. 08/770,491, filed Dec. 20, 1996 andU.S. Pat. No. 6,201,601, both of which are incorporated in theirentireties by reference. To simplify the figure, some of the opticalcomponents of the system have been omitted, such as components directingthe illumination beams to the wafer. The wafer 20 inspected isilluminated by a normal incidence beam 22 and/or an oblique incidencebeam 24. Wafer 20 is supported on a chuck 26 which is rotated by meansof a motor 28 and translated in a direction by gear 30 so that beams 22and/or 24 illuminates an area or spot 20 a which is caused to move andtrace a spiral path on the surface of wafer 20 to inspect the surface ofthe wafer. Motor 28 and gear 30 are controlled by controller 32 in amanner known to those skilled in the art. Alternatively, the beam(s) 22,24 may be caused to move in a manner known to those skilled in the artto trace the spiral path or another type of scan path.

[0041] The area or spot 20 a illuminated by either one or both beams onwafer 20 scatters radiation from the beam(s). The radiation scattered byarea 20 a along directions close to a line 36 perpendicular to thesurface of the wafer and passing through the area 20 a is collected andfocused by lens collector 38 and directed to a PMT 40. Since lens 38collects the scattered radiation along directions close to the normaldirection, such collection channel is referred to herein as the narrowchannel and PMT 40 as the dark field narrow PMT. When desired, one ormore polarizers 42 may be placed in the path of the collected radiationin the narrow channel.

[0042] Radiation scattered by spot 20 a of wafer 20, illuminated byeither one or both beams 22, 24, along directions away from the normaldirection 36 is collected by an ellipsoidal collector 52 and focusedthrough an aperture 54 and optional polarizers 56 to dark field PMT 60.Since the ellipsoidal collector 52 collects scattered radiation alongdirections at wider angles from the normal direction 36 than lens 38,such collection channel is referred to as the wide channel. The outputsof detectors 40, 60 are supplied to a computer 62 for processing thesignals and determining the presence of anomalies and theircharacteristics.

[0043] The SP1^(TBI) system is advantageous for unpatterned waferinspection since the collection optics (lens 38 and mirror 52) isrotationally symmetric about the normal direction 36, so that theorientation of the system in FIG. 1 relative to the orientation ofdefects on the surface of wafer 20 is immaterial. In addition, theangular coverage of the scattering space by these collectors is wellmatched to those required to detect the anomalies of interest inunpatterned wafer inspection applications.

[0044] In addition to the above characteristic, however, the SP1^(TBI)system 10 has another important characteristic in that both its lenscollector 38 and the ellipsoidal mirror collector 52 preserve theazimuthal information contained in radiation scattered by defects onsurface of wafer 20. Thus, certain defects and/or pattern on the wafermay scatter radiation preferentially along certain azimuthal directionsmore than other azimuthal directions. By making use of the preservedazimuthal information in the collected radiation by the collectors 38and 52, system 10 may be advantageously adapted and modified for thedetection of defects on patterned wafers.

[0045] One aspect of the invention is based on the recognition that, bysegmenting the radiation collected by the lens 38 and/or ellipsoidalmirror 52, radiation scattered in different azimuthal directions may bedetected separately. In this manner, the detectors detecting radiationdiffracted or scattered by pattern may become saturated, while otherdetectors not detecting such diffraction or scatter will yield usefulsignals for the detection and classification of defects on wafer 20.Since the lens 38 and ellipsoidal mirror 52 preserve the azimuthalinformation of the scattered radiation, knowledge of the type of patternor defects present on wafer 20 can be advantageously used to design andposition multiple detectors to advantageously detect and classify thedefects on the wafer. This is especially true in the case of regularpatterns such as memory structures on wafer 20, as will be explainedbelow, since radiation diffracted by such regular patterns also tend tobe regular.

[0046]FIG. 2 is a schematic view illustrating a convergent hollow coneof radiation which can be collected by lens 38 or mirror 52. In the caseof lens 38 of FIG. 1, a spatial filter (not shown in FIG. 1) is employedto block the specular reflection of the normal incidence beam 22 fromreaching detector 40, so that the radiation focused by lens 38 to PMT 40has the shape of a convergent hollow cone illustrated in FIG. 2. In thecase of the ellipsoidal mirror 52, since the mirror is not a completeellipse, it collects only radiation scattered at larger angles to thenormal direction 36 without also collecting the radiation scattered atnear normal directions, so that the radiation focused by mirror 52towards detector 60 also has the shape of a convergent hollow cone asshown in FIG. 2.

[0047]FIG. 3A is a schematic view of a possible arrangement of multiplefiber channels receiving radiation in the convergent cone of radiationshown in FIG. 2, such as that collected by mirror 52, to illustrate thepreferred embodiment of the invention. The arrangement in FIG. 3Acomprises two substantially concentric rings of optical fiber channels72 that are used to carry the collected scattered radiation in theconvergent hollow cone shown in FIG. 2. Fourier components or otherpattern scattering from the pattern on the wafer 20 may reach some ofthe fibers 72, thereby causing the detectors detecting the radiationfrom such channels to be saturated. However, there will be other opticalfiber channels that do not receive such unwanted pattern scattering. Theuse of multiple fiber channels 72 effectively segments the collectedscattered radiation into different sectors or segments so that only someof the fiber channels will receive a strong signal and can becomesaturated due to the Fourier or other pattern scatter leaving theremaining channels carrying information that can be analyzed fordetecting anomalies. As will be explained below, since the azimuthalinformation in the collected scattered radiation in the cone of FIG. 2is preserved, various schemes may be employed to minimize the effects ofthe pattern scatter when the segmented approach of FIG. 3A is used.

[0048] Different types of detectors may be used to detect the radiationcarried by the fiber channels 72, such as the multi-anode PMT shown inFIG. 3B. In the event multi-anode PMT is used, however, there is anominal three percent cross-talk between any two adjacent channels. Toavoid such cross-talk, fibers 72 may be aligned with every other PMTanode, in a manner illustrated in FIG. 3B. FIG. 3B is a schematic viewof a multi-anode PMT. As shown in FIG. 3B, only the anodes 74 that areshaded are aligned with fibers 72, where anodes 76 are not aligned withany of the fibers 72. This avoids the three percent cross-talk that maybe present if all of the anodes shown in FIG. 3B are aligned with fibers72.

[0049]FIG. 4 is a schematic view illustrating an arrangement 80 of fiberchannels or multiple detectors 82 for the narrow channel. Thus, fibersor detectors 82 may be aligned with the collected scattered radiationillustrated in FIG. 2 for the narrow channel collected by lens 38 forsegmenting the radiation in a similar manner as that described above forthe wide channel.

[0050]FIG. 5A is a partially cross-sectional view and partiallyschematic view of a defect inspection system to illustrate the preferredembodiment of the invention. To simplify FIG. 5A, the two illuminationbeams 22 and 24, computer 62 and the mechanisms for moving the wafer arenot shown in the figure. Radiation scattered by spot 20 a on wafer 20and collected by lens 38 is reflected by mirror 102 to detector 40. Stop104 blocks the specular reflection of the normal incident beam 22 fromdetector 40 and results in a cone shape of the convergent beam in FIG.2. The beam collected and focused by lens 38 and reflected by mirror 102passes through a beam splitter 106 and a portion of the collectedradiation that passes through the beamsplitter is focused onto detector40 to provide a single output as would be the case in normal SP1^(TBI)operation. Beamsplitter 106 reflects and diverts a portion of thecollected radiation from lens 38 to the arrangement 80 of optical fibersof FIG. 4. Preferably, the size of optical fibers 82 and the size of thehollow cone reflected by beamsplitter 106 are such that fibers 82collect and convey most of the radiation in the hollow cone ofradiation. Each of the fibers 82 is then connected to a correspondingdetector or a detecting unit in a multi-unit or multi-element detector.In a similar manner, beamsplitter 112 diverts a small portion of theradiation collected by ellipsoidal mirror 52 towards arrangement 70′ ofoptical fiber channels 72, shown more clearly in FIG. 5B, where eachchannel 72 is connected to a separate detector or a separate detectingunit in a multi-element detector system (not shown). As shown in FIG.5A, beamsplitter 112 is such that it diverts radiation only within anarrow ring 114 to arrangement 70′. Most of the radiation collected bymirror 52 is passed through beamsplitter 112 and focused to detector 60to provide a single output as would be the case in normal SP1^(TBI)operation. In FIG. 5A, the illumination beams 22, 24 and the mechanismsfor moving the wafer have been omitted to simplify the figure.

[0051] As will be evident from a comparison of system 10 of FIG. 1 andsystem 100 of FIG. 5A, system 100 retains substantially all of thefeatures of system 10 of FIG. 1. In addition, system 100 diverts aportion of the scattered radiation collected by each of lens 38 andmirror 52, and directs them towards fibers 82, 72 to convey thesegmented radiation to a separate detectors or detecting units. Thesystem is compact and requires minimal additional space compared to theSP1^(TBI) system 10 of FIG. 1. In this manner, a single combinedinstrument may be optimized and used for both unpatterned and patternedwafer inspection, thereby eliminating the need for two separateinstruments for the two types of wafer inspection.

[0052] When only patterned wafers are to be inspected, an alternativedefect inspection system 150 of FIG. 6A may be used. In FIG. 6A, theillumination beams 22, 24, computer 62 and the mechanisms for moving thewafer have been omitted to simplify the figure. As shown in FIG. 6A,scattered radiation collected by lens 38 and by mirror 52 are reflectedby mirror 112′ towards an arrangement of optical fibers 152 which isshown more clearly in cross-section in FIG. 6B. As shown in FIG. 6B,arrangement 152 includes a ring of fibers 82 conveying scatteredradiation collected by lens 38 and a ring of fibers 72 conveyingscattered radiation collected by mirror 52. As before, each of thefibers 72, 82 are connected to a separate detector or a detecting unitof a multi-unit detector.

[0053] While a single ring of detectors are shown in FIGS. 4 and 5B,multiple rings may be employed such as that shown in FIG. 3A. Theoptically transmissive cores of optical fibers that are located adjacentto each other in each of the two arrangements 70, 70′, 80 are separatedfrom each other by the claddings that envelope the cores so thatcrosstalk between adjacent cores is reduced. Obviously, optical channelsother than fibers may be used and are within the scope of thisinvention. Where such channels do not include separators such as thecladding in the case of optical fibers, other optical separators may beemployed to reduce crosstalk.

[0054] In reference to FIG. 5A, while the diversion of some of thecollected scattered radiation from detectors 40 and 60 may reducesomewhat the particle sensitivity of system 100 when inspectingunpatterned wafers, such reduction is not significant due to the highefficiency of the narrow and wide collection channels of system 100. Ifdesired, when inspecting unpatterned wafers, radiation conveyed byfibers 72 and 82 may be directed towards detectors 40 and 60,respectively, to substantially restore the sensitivity of system 100 sothat the resulting sensitivity is substantially the same as that ofsystem 19 of FIG. 1.

[0055] Systems 100 and 150 of FIGS. 5A and 6A are particularlyadvantageous for distinguishing between micro-scratches and particles.The scattering pattern due to a micro-scratch gives the highestconcentration of energy and greatest detection uniformity whenilluminated normally and captured in the near normal or narrow channelcollected by lens 38. The unique signature of the scratch in the form ofan elongated pattern in the far-field, allows for a simple method ofclassification. Therefore, if the eight or more fibers 82 arrange in aring format is placed in the path of the hollow cone of light focused bylens 38 towards fibers 82 as diverted by beamsplitter 106, where theoutputs of these fibers are directed onto a multi-channel detector or anarray of individual detectors, by simple process of comparing thesignals obtained through any two diagonally opposed fibers relative tothe signals in the remaining fibers, the presence of the micro-scratchis obtained. When illuminated obliquely, micro-scratches result inscattering patterns which can be distinguished from those due toparticles, by using the multiple detection channels that were describedabove in conjunction with pattern inspection, viz. multiple fiber units70 and 70′. In both the wide and narrow channels, it is also possible toplace individual detectors or multi-element detecting systems directlyin the path of the converging hollow cone of light, rather thanindividual optical fibers.

ARRAY WAFERS

[0056] Where systems 100, 150 are used for inspecting wafers with memorycells thereon, the Fourier components from the memory array will spin asthe wafer is rotated. These components will thus rotate and be atdifferent azimuthal angles about the normal direction 36 of FIGS. 1, 5Aand 6A. This means that these Fourier components will be conveyed bydifferent fibers 72, 82 as the wafer is rotated. Since the array ofmemory cells may have different dimensions in the X and Y directions ofthe wafer, as the wafer rotates, the number of detectors that aresaturated by the Fourier components will change. This can be providedfor by knowing the X and Y dimensions of the memory cells so that thenumber of Fourier diffraction components can be estimated.Alternatively, during an initialization process at the beginning, alearn cycle is performed where the maximum number of Fourier componentsthat need to be eliminated is determined by noting the maximum number ofdetectors with very strong, or saturated, outputs. During the subsequentmeasurement, this number of detector outputs may then be eliminated,where the outputs eliminated are the ones that are saturated or the onesthat have the largest values. In the case of a multi-anode PMT, forexample, where each anode is used and is connected to a correspondingfiber, cross-talk may be reduced by also eliminating the componentsadjacent to the detectors having the highest outputs. For example, ifthe wafer in one position gives three Fourier components, and in anothertwo, the three direct components together with two components adjacentto each would be eliminated for a total of nine detector outputs thatare eliminated. This leaves seven useable detector outputs. This numberwill be maintained regardless of the exact orientation of the wafer.This allows the user to maintain the sizing option for the particles.

[0057] Preferably the fibers 72 and 82 are arranged rotationallysymmetrically around a direction, such as axes 74 and 84 shown in FIGS.3A, 4, 5B and 6B. When arranged in such manner, the radiation scatteringdirections are partitioned into identical angular segments and radiationscattered within each segment is collected by a corresponding fiber.When beamsplitter or mirror 102, 112, 112′ reflects or diverts a portionof the radiation collected by lens 38 or mirror 52, the azimuthalpositions of the collected scattered radiation is preserved when thereflected or diverted radiation is directed to the fibers 72, 82. Whensuch radiation is so reflected or diverted, axes 74, 84 correspond tothe normal direction 36, and the azimuthal positions of the collectedscattered radiation about the axes 74, 84 corresponding to theirazimuthal positions about the normal direction 36 are preserved.

[0058] As described above, azimuthal characterizations of scatteredradiation are preserved both for the narrow and the wide channels. Thescattering pattern due to a micro-scratch illuminated by beam 22 in asubstantially normal illumination direction gives the highestconcentration of energy and the greatest detector uniformity whencaptured in the narrow channel. Furthermore, the unique signature of ascratch in the shape of an elongated pattern in the far-field allows fora simple method of classification. In reference to FIG. 4, for example,when the eight fibers 82 in arrangement 80 are used to receive and carrythe scattered radiation in the hollow cone of light of FIG. 2 collectedby lens 38, where the fibers are each connected to an individualdetector, the sum of the two signals from any two diametrically opposedfibers may be compared with the output signals of the remainingdetectors to ascertain the presence of a micro-scratch.

[0059] As explained above, if all of the scattered radiation fromilluminated spot 20 a is collected and directed to a single detector,the presence of Fourier or other scatter components will cause thedetector to saturate so that the system will not be able to provideuseful information concerning anomalies in the illuminated spot. Forthis reason, applicants propose segmenting the collected scatteredradiation into different segments. If the collected scattered radiationis divided into very few segments, such as two or three, resulting intwo or three output signals, the probability may be high that the two orthree segments would still contain pattern scatter so that the two orthree detectors would again become saturated and yield no usefulinformation concerning anomalies. Thus, to be useful, the segmentationis preferably fine enough that at least some of the detector signalscontain no significant pattern scatter. Thus, if lines joining variousFourier or other scatter components to the normal direction 36 do notget closer to each other angularly than δφ, it is preferable for thesegmentation to be such that each detector receives scattered radiationcollected within an angular aperture of no more than δφ. In this manner,one can be assured that there will be at least some detectors that willreceive no Fourier or other pattern scatter and will yield outputsignals that are useful for ascertaining the presence of, or thecharacterization of, defects on the sample surface. Where the segmentedradiation is conveyed to multiple optical fibers, it is, therefore,preferable for at least some of the fibers to receive radiationcollected within azimuthal angles of no more than δφ.

[0060] Another arrangement for segmenting the collection of thescattered radiation is illustrated in FIG. 7. FIG. 7 is a top view of arotationally symmetric collector such as an ellipsoidal or paraboloidalmirror 200 with two apertures 202, 204, where the two apertures arepreferably centered at +90 and −90 azimuthal positions relative to theoblique beam 24 illustrated in FIG. 1 and 7. A multi-element detector ordetector array 206, 208, is placed in each of the two apertures, wherethe detector or array may be a multi-anode PMT or multi-PIN diode array.FIG. 8A is a schematic side view of a portion of the detector ordetector array 206, 208 of FIG. 7 along arrow 8A. As shown in FIG. 8A,each of the detecting units 206 a, 208 a has a substantially rectangularshape, with width w. Preferably, the units 206 a, 208 a are arrangedsubstantially with their elongated sides parallel to the normaldirection 36. In this manner, each of the detecting units 206 a, 208 acollects scattered radiation within a small angular sector subtended bythe widths of the elongated elements 206 a, 208 a towards the centeraxis 36 where the angle of such sector subtended is no more than δφ, sothat at least some of the detectors would provide useful signals fordetecting and characterizing anomalies on the sample surface withoutbeing masked by pattern scatter.

[0061] By placing two detector or detector arrays 206, 208 at theapertures 202, 204, respectively, the detector units 206 a, 208 a willprovide useful signal components for detecting anomalies. Theabove-described process of either estimating or determining through aquick learn cycle may be applied to the two detector or detector arrays206, 208 for ascertaining the maximum number of pattern scattercomponents that need to be eliminated, so that the remaining detectorsignals can then be used for detecting anomalies.

[0062] The size of the semiconductor circuits is continually beingreduced. Thus, when the cell size is reduced, this correspondinglyreduces the number of Fourier or other scatter components. For largercell sizes, if the width w of the detecting units of detectors ordetector arrays 206, 208 are not reduced, each of the detecting units inthe two detectors or detector arrays 206, 208 will become saturated sothat again no useful signal results. This can be remedied by the schemeillustrated in FIG. 8B.

[0063] It is possible to further enhance the signal gathering capabilityof the detectors or detector arrays 206, 208 as illustrated in FIG. 8B.In the event that the number of pattern scatter increases beyond whatthe detectors or detector arrays were designed for, using thearrangement of FIG. 8B allows anomaly detection despite such increase.As shown in FIG. 8B, the multiple detecting units of detectors or thedetector arrays 206, 208 are labeled from the same side to the other;D1, D2 . . . D2 n, D2 n+1 . . .. The odd numbered detecting units D1,D3, D5 . . . D2 n+1 . . . of multi-unit detector or detector array 206are masked by a spatial filter 216. The even numbered detecting unitsD2, D4, D6 . . . D2 n . . . of detector or array 208 are masked by aspatial filter 218 as shown in FIG. 8B. In this manner, as relativerotation motion is caused between the sample surface and detectors orarrays 206, 208, the detecting units that are not covered would stillprovide useful signals.

[0064]FIG. 9A is a cross-sectional view of collector 52 of FIG. 1modified to include the type of apertures or detector or detector arraysillustrated in FIGS. 7, 8A and 8B. The two apertures 202, 204 are,preferably, of a size such that each aperture comprises an azimuthal gapof about 10°-40° on each side centered on ±90° azimuth. The aperturesare located only towards the bottom portion of the collector so thatonly scattered radiation along directions close to the surface aredetected by the detectors or detector arrays 206, 208. Two lenses 222,224 with the appropriate F numbers are used for collecting and focusingthe scattered radiation from the illuminated spot 20 a to theirrespective detector or detector array 206, 208. The two detector ordetector arrays may be placed at the back focal planes of the two lenses222, 224.

[0065] The masks 216, 218 may be placed between the illuminated spot 20a and the detectors or detector arrays 206, 208 by means of filterwheels 226, 228 rotated by actuators 232, 234 in a manner known to thoseskilled in the art so that the connections between these two actuatorsand the wheels are not shown and a detailed description of theiroperation is not necessary herein. For simplicity, only the maskportions 216, 218 of the two filter wheels 226, 228 are illustrated inFIG. 9A. The features illustrated in FIGS. 9A, 9B and 9C may be combinedwith the systems 100, 150 of FIGS. 5A and 6A to further increase theirversatility. When the combined instrument is used for the inspection ofunpatterned or bare wafers, for example, reduction in sensitivity due tothe two apertures 202, 204 is not significant. Furthermore, the outputsof detectors or detector arrays 206, 208 can obviously be added to theoutput of detector 60 at least partially to restore the sensitivity ofthe system when inspecting unpatterned wafers. To suppress extraneoussignals caused by film roughness, the feature of FIGS. 9A-9C may beadvantageously used as well. Since film roughness scatters P-polarizedlight more efficiently than S-polarized light, in such circumstances, itwill be desirable to supply an oblique illumination beam 24 which isS-polarized, and collect only the S-polarized scatter from illuminatedspot 20 a. This may be accomplished conveniently by means of filterwheels 226, 228. Actuators 232, 234 may be used to rotate the filterwheels 226, 228 so that a S-polarizer 236 would take the place of mask216 and another S-polarizer would take the place of mask 218 in FIG. 9A.As will be noted from FIG. 9A, this arrangement is advantageous sincethe two filters 236, 238 are located close to the surface of wafer 20 sothat the collected radiation is confined to scattering angles that arevery close to the wafer surface. In the case of very rough films, tofurther restrict the collection elevation angles, the upper half of theS-polarizer may be blocked by using the semi-circular opaque screen236′, 238′ in the filter wheel. For example, the semi-circularS-polarizer may restrict the elevational collection angles of theaperture to within a range of about 55 to 70° from the normal direction36. This is helpful since the amount of scatter caused by film roughnessincreases with the elevation angles to the wafer surface. FIG. 9Cillustrates an alternative filter wheel that may be used for theinspection of bare or unpatterned wafers.

[0066] If the directions of the expected pattern scatter surface areknown, spatial filters may be designed to block such scattering, therebydetecting only the scatter by anomalies on the surface. FIG. 10 is aschematic view illustrating the two-dimensional Fourier components of anarray structure when illuminated with normal incidence radiation. As thesample rotates, all of the spots at the intersections of the X-Y lineswill rotate, thereby generating circles. These circles represent theloci of the Fourier components as the wafer is rotated. The dark opaquecircle at the center is the 0-5° blockage of the collection space causedby stop 104 in FIG. 5A. From FIG. 10, it is noted that there are gaps inbetween the circles where there are no Fourier components. At least intheory, it is possible to construct a programmable filter (e.g. a liquidcrystal filter) in which annular bands of arbitrary radii are blockedout. A simple spatial filter may be constructed also to achieve many ofthe objectives herein. Thus, if the cell size of a regular memory arrayon the wafer is such that its X and Y dimensions are not larger thanabout 3.5 microns, for example, this means that for 488 nanometerswavelength radiation used in the illumination beams 22, 24, the firstFourier component is at about 8° to the normal direction 36. Therefore,if a spatial filter is employed, blocking all collected radiation in thenarrow channel that is at 8° or more to the normal direction 36 willleave an annular gap of 2 or 3° ranging from the rim of the centralobscuration (i.e. 5 or 6°) to the rim of the variable aperture at about8°. Under these conditions, as the wafer spins, no Fourier componentscan possibly get through the annual gap and scatter from the array issuppressed. In one embodiment, the spatial filter used leaves an annulargap between about 5 to 9° from the normal direction 36.

[0067] In the example above, a spatial filter is designed for the narrowchannel; it will be understood that similar spatial filters may bedesigned for the wide channel as well. Such and other variations arewithin the scope of the invention.

[0068] As explained above, in order to assure that at least somedetectors will receive useful signals that are not masked by Fourier orother pattern scatter, the collection aperture of at least some of thedetectors are preferably no larger than the angular separation betweenthe expected pattern scatter. For this purpose, a spatial filter may beconstructed where all of the collected radiation in the narrow or widechannel is blocked except for a small angular aperture where the angleof the angular aperture is not larger than the angular separationbetween pattern scatter. When such a spatial filter is placed betweenilluminated spot 20 a and the detector, such as detector 40 or 60, theFourier components will spin in and out of this little opening. Whenthere is no component going through, the data will be valid fordetection of anomalies. Otherwise, the signal will be very strong, oreven saturated. Thus, at the end of the spiral scan, the wafer map willbe a series of data-valid, and saturated sectors. If the scan isrepeated a second time where the center position of the angular apertureis shifted relative to its position during the first scan by the minimumangular separation of the patterned scatter, one would again obtain asimilar map comprising data-valid and saturated sectors as before.However, in those areas that were saturated during the first scan, onenow has valid data. Therefore, by combining the two data sets using thelogical OR operation, a full wafer map of valid data can be achieved.

[0069] The above process can be simplified by employing an asymmetricmask 250 illustrated in FIG. 11. As shown in FIG. 11, the two sectorshaped apertures 252, 254 are offset from a diametrically oppositeposition by an angle which is equal to the expected minimum angularseparation of pattern scatter. When such a filter is placed between theilluminated spot 20 a and detector 40 or 60 of FIG. 1, the detectors 40and 60 will then provide a full wafer map when the wafer is scanned.

[0070]FIG. 12 is a schematic view of a defect detection systemillustrating another alternative embodiment of the invention. As shownin FIG. 12, when illuminated by beams (not shown), such as beams 22, 24of FIG. 1, the scattered radiation collected by collector 52 (omittedfrom FIG. 12 to simplify the figure) are focused to a triangular-shapeddevice 262 having two mirrors 262 a, 262 b on opposite sides of thedevice. The illumination beams have also been omitted for simplicity.The scattered radiation are, therefore, reflected into two oppositehemispheres by device 262. Mirror 262 a reflects half of the scatteredradiation towards PMT1 and mirror 262 b reflects the other half ofscattered radiation towards PMT2 and asymmetric mask 250 may be employedbetween mirror 262 a and PMT1 and between mirror 262 b and PMT2. In thismanner, the two PMTs will provide two wafer maps useful for anomalydetection and classification.

DETECTION OF CMP DEFECTS

[0071] One aspect of this invention covers two algorithms forclassifying CMP defects. The first method is based on the spatialdistribution of the light scattered by defects. Theoretical simulationand experimental results indicate that the light scattered by CMPmicro-scratches is primarily in the direction of specular reflectionwhile light scattered by particles (especially, small particles) has adifferent spatial distribution. As a result, defect classification canbe achieved by measuring the distribution of the scattered light. It canbe implemented by using two or more detectors placed at proper positionsaround the scatterers. Or, using one detector with two or more spatialfilters/masks. Three different ways of implementing this algorithm areset forth below.

[0072] The second algorithm is based on a dual-polarization method. Thismethod compares the scattering signal from a defect using incident S andP polarized beams. Theoretical simulation indicates that the scatteringintensity is proportional to the local interference intensity seen bythe defects. This interference intensity is different for S and Ppolarized light and has a dependence on the height above the wafersurface. Thus, the interference intensity seen by a particle (anabove-surface defect) is very different from that seen by amicro-scratch (at or below the wafer surface). Defect classification canbe achieved by comparing the scattering signal strength using both S andP polarized incident light or radiation.

DETAILS OF OPERATIONS

[0073] In the following paragraphs, we describe theimplementations/operations of the inventions in a Surfscan SP1^(TBI)system. However, the algorithms are not limited to the SP1^(TBI) system.They can be implemented in any optical scattering tool. For all thealgorithms described below, PSL calibration curves for all the utilizedchannels are required. They are crucial to the success of theclassification of CMP defects.

[0074] Algorithm #1, implementation #1, dual-channels, oblique incidenceand one scan:

[0075] There are four dark field channels in an SP1 system: DWN, DNN,DWO and DNO, where DWN stands for the channel carrying scatteredradiation collected by the ellipsoidal mirror originating from a normalillumination beam, DNN for the channel carrying scattered radiationcollected by the lens collector originating from a normal illuminationbeam, DWO for the channel carrying scattered radiation collected by theellipsoidal mirror originating from an oblique illumination beam, andDNO for the channel carrying scattered radiation collected by the lenscollector originating from an oblique illumination beam. Thedual-channel method uses two dark-field channels, for example the DWOand the DNO channels. The principle of this method is based on the factthat particles and micro-scratches have different spatial scatteringpatterns. A particle scatters light in all directions, which can becollected by both dark-field channels. However, a micro-scratchpreferentially scatters light in certain directions, resulting in thesignal captured in one channel being significantly larger than that inthe other channel. For example, when the oblique channels DWO and DNOare used, micro-scratches are preferentially captured in the DWO channelor the signal in DWO channel is significantly larger than that in DNOchannel. To differentiate micro-scratches from particles, we calculatethe size ratio of each defect captured in DWO and DNO channels. If thesize ratio for a defect is close to one, it is classified as a particle.However, if the size ratio of a defect is less than certain fractionnumber (example: 0.8), it is classified as a micro-scratch. If a defectis only captured in DWO channel but not in DNO channel, it is classifiedas a CMP micro-scratch. If a defect is only captured in DNO channel butnot in DWO channel, it is classified as a particle.

[0076] Algorithm #1, implementation #2, dual-channels, normal incidenceand one scan:

[0077] The implementation in normal channels is similar to that inoblique channels. The difference is that the light scattered from a CMPmicro-scratch is preferentially towards narrow channel (DNN) in normalincidence instead of wide (DWN) channel. This is consistent with thefact that CMP micro-scratches scatter light preferentially towards thedirection of specular reflection. The defect classification is achievedby calculating the size ratio of a defect captured in both DNN and DWNchannels. If the size ratio for a defect is close to one, it isclassified as a particle. However, if the size ratio of a defect islarger than certain number (example: 1.6), it is classified as amicro-scratch. If a defect is only captured in DNN channel but not inDWN channel, it is classified as a CMP micro-scratch. If a defect isonly captured in DWN channel but not in DNN channel, it is classified asa particle.

[0078] Algorithm #1, implementation #3, single-channel, obliqueincidence, two masks and dual-scans:

[0079] The third method of implementing algorithm #1 uses two masks. Oneof the masks (#1) is designed to capture preferentially the scatter fromCMP micro-scratches; this mask is illustrated in FIG. 13A, where theshaded region indicates the area where radiation is blocked, and thenon-shaded region indicates the area where radiation transmittance isallowed. The other one (#2) is designed to block the light scattered byCMP micro-scratches; this mask is illustrated in FIG. 13B, where theshaded region indicates the area where radiation is blocked, and thenon-shaded region indicates the area where radiation transmittance isallowed. The calibration curves of both mask configurations are needed.The defect classification is achieved by calculating the size ratio of adefect captured in both mask configurations. For a given defect, if thesize ratio of mask#1 and mask#2 is close to one, it is classified as aparticle. However, if the size ratio of a defect is larger than certainnumber (example: 1.15), it is classified as a micro-scratch.. If adefect is only captured in mask#1 configuration but not in mask#2configuration, it is classified as a CMP micro-scratch. If a defect isonly captured in mask#2 configuration but not in mask#1 configuration,it is classified as a particle.

[0080] Algorithm #1 can also be implemented with a multi-anode PMT. Theadvantage of this method is that it can be done in one scan. It isessentially the same as using two masks, but only one scan is needed fordata collection.

[0081] Algorithm #2, implementation #1, single-channel,dual-polarizations, oblique incidence and dual scan:

[0082] Algorithm #2 utilizes two incident polarizations, S and P. Twoscans are needed for this method. One is for S-polarization; the otheris for P-polarization. The PSL calibration curves for both S- and P-polarizations are used. The defect classification is achieved bycalculating the size ratio of a defect captured in both P and S scans.If the size ratio of P and S scans is close to one, it is classified asa particle. However, if the size ratio of a defect is other than one(example: <0.65 or >1.85 depending on film thickness), it is classifiedas a micro-scratch. For a dielectric film, the interference intensityfor the two polarizations will vary with film thickness. The changes ininterference intensity of the two polarizations are out of phase; whenthe P polarization interference intensity is at a maximum, the Spolarization interference intensity will be at a minimum and vice versa.Thus, the size ratio for CMP defects will either be greater or less than1.0 depending upon the thickness of the dielectric film. Similarly, if adefect is captured only in one polarization but not the other, it isclassified as a CMP micro-scratch or particle depending on the filmthickness. This method has been successfully demonstrated using oxideCMP wafers. This method is expected to work better for metal films thanthick dielectric films since thickness variation across the wafer is nota concern for most metal film with practical thicknesses.

[0083] In one experiment, the SP1™ instrument is calibrated using PSLspheres so that the size ratio of the detected intensities during the Pand S scans is normalized to 1 for particles. Thus, the particlespresent would give rise to ratios at or around 1. In addition, from ahistogram provided by the instrument, a second set of intensity ratiosclusters at a value greater than 1, indicating a set of defects thatscatter more in response to P-polarized illumination than S-polarizedillumination. These are CMP defects such as micro-scratches; this wouldbe true even where scattered intensities are detected only during the Pscan and not during S scan since in that instance the ratio is infiniteand therefore greater than 1. A third group of ratios are at zero orclose to zero values. These are deemed to indicate particles, for thereasons explained below.

[0084] Interference effects at the surface inspected when illuminated byP- or S-polarized radiation cause the scattered intensity detected to bestronger during a P scan compared to that during a S scan, or viceversa. Thus, in the experiment above, if the interference effects at thesurface are such as to cause the scattered intensity detected to bestronger during a P scan compared to that during a S scan, onlyparticles large enough will be in a region where S polarization isexperiencing constructive interference. This is illustrated, forexample, in FIG. 14. For example, in reference to FIG. 14, if the filmthickness at the wafer surface is 200 nanometers, from the curves inFIG. 14, one would expect the interference intensity at the wafersurface to be much stronger when illuminated by P-polarized radiationthen when it is illuminated by S-polarized radiation. However, particles300 nanometers or above would cause the scattered intensity detectedduring a S scan to be much stronger than that during a P scan.

SURFACE ROUGHNESS DETERMINATION

[0085] For opaque films such as metals and transparent dielectrics suchas dielectrics with low k (both spun on a CVD deposited), haze measuredfrom the films varies with surface roughness of the films if there islittle film thickness variation. Most dielectric films CVD deposited forintegrated circuit applications are quite uniform. Hence, hazemeasurements may provide a quick alternative to the measurement of filmroughness.

[0086] Surface roughness is typically measured by instruments such asthe HRP® tool from KLA-Tencor Corporation of San Jose, Calif., andatomic force microscope or any other type of scanning probe microscopessuch as near field microscopes or scanning tunneling microscopes. Such aprocess is slow. By making use of the above relationship that haze haswith film roughness for uniform dielectric films, or metals of a widevariety of uniformity film roughness can be measured much more quicklythan conventional methods. Thus, in reference to FIG. 16, a database maybe constructed by measuring surface roughness of representative films302 of different thicknesses using the KLA-Tencor High ResolutionProfiler, or AFM type tool 304, and measuring haze values of these samefilms using the SP1^(TBI) system 10, or one of the combined systems(e.g. 100) described above or any other tool that can be used to measurehaze, in order to build a database using computer 310 of the correlationbetween haze and surface roughness for films of different thicknesses.Measurement of like films of various thicknesses may be preferable sincesurface roughness increases with film thickness. A database may then beconstructed such as the graphical plot shown in FIG. 15. Then if it isdesirable to determine the surface roughness of an unknown film, itsroughness may be determined by measuring the haze of the film using aninstrument such as system 10 of FIG. 1 or the combined instrumentsdescribed above. The haze measurement is then used to select acorresponding roughness value from the database for a film of knownthickness, such as from the graph shown in FIG. 15. This will save theend user in the fabrication facility up to an hour for each film sinceit takes only about one minute to measure the haze value and correlatethe haze measurement with the RMS roughness calibration curve of FIG.15.

[0087] While the invention has been described above by reference tovarious embodiments, it will be understood that changes andmodifications may be made without departing from the scope of theinvention, which is to be defined only by the appended claims and theirequivalents. All references mentioned herein are incorporated in theirentireties by reference.

What is claimed is:
 1. A surface inspection method for detectinganomalies on a surface, comprising: causing the surface to be scanned bya beam of radiation; collecting radiation scattered from the surface bymeans of a collector that collects the scattered radiation substantiallysymmetrically about a line normal to the surface; directing thecollected radiation to channels at different azimuthal angles about theline or about a direction corresponding thereto so that informationrelated to relative azimuthal positions of the collected radiation aboutthe line is preserved and radiation scattered by the surface atdifferent azimuthal angles with respect to the line is conveyed alongdifferent channels, said directing including separating the channelsfrom each other by separators to reduce crosstalk; converting thecollected radiation carried by at least some of the channels intorespective signals representative of radiation scattered at differentazimuthal angles about the line; and determining the presence and/orcharacteristics of anomalies in or on the surface from said signals. 2.The method of claim 1, wherein said directing includes supplying thecollected radiation to optical fibers that serve as the channels.
 3. Themethod of claim 1, wherein said directing includes reflecting a portionof the collected radiation at different azimuthal angles from areflective collector towards the channels.
 4. The method of claim 1,wherein said directing includes supplying a first portion of thecollected radiation at different azimuthal angles from the collectortowards a detector to provide a single output, and a second portion ofthe collected radiation at different azimuthal angles from the collectortowards the channels.
 5. The method of claim 1, wherein said directingincludes supplying the collected radiation substantially symmetricallyabout the line or the direction to the channels.
 6. The method of claim1, further comprising providing the channels so that they aresubstantially symmetrically disposed about the line or the direction. 7.The method of claim 6, wherein said directing directs the collectedradiation to detection units of a multiunit detector, where the unitsreceiving the collected radiation are separated from one another by atleast one detection unit to reduce crosstalk.
 8. The method of claim 6,wherein said converting converts the collected radiation from at leasttwo diametrically disposed channels, said method further comprisingcomparing signals converted from said at least two diametricallydisposed channels to detect micro-scratches on the surface.
 9. Themethod of claim 1, wherein said providing provides the channels so thatthey are at elevation angles away from any expected components scatteredby a pattern on the surface.
 10. The method of claim 9, furthercomprising determining from the dimensions of the pattern the elevationangles of the expected components scattered by the pattern.
 11. Themethod of claim 9, wherein said providing provides the channels so thatthey are substantially at elevation angles between about 5 and 9 degreesfrom the line or the direction.
 12. The method of claim 9, wherein saidexpected components scattered by the pattern are Fourier components. 13.The method of claim 1, further comprising determining from the signalsthe number of Fourier components scattered by any regular pattern on thesurface, discarding a number of signals related to such number and usingthe remaining signals for detecting anomalies on the surface.
 14. Asurface inspection method for detecting anomalies on a surface having adiffracting pattern thereon that scatter radiation, said methodcomprising: causing the surface to be scanned by a beam of radiation;collecting radiation scattered from the surface by means of a collectorthat collects the scattered radiation substantially symmetrically abouta line normal to the surface; filtering at least a portion of thecollected radiation by means of a spatial filter having an angular gaptherein of an angle related to the angular separation of expectedradiation components scattered by the pattern on the surface; anddetermining the presence of anomalies in or on the surface from saidfiltered collected radiation.
 15. The method of claim 14, wherein saidfiltering filters the collected radiation by means of two correspondingspatial filters each having an angular gap therein, the gaps offsetrelative to each other by an angle related to the angular separations ofthe expected components scattered by the pattern on the surface.
 16. Themethod of claim 15, further comprising dividing the collected radiationinto a first and a second portion, wherein said filtering filters thefirst and second portions by means of the two corresponding spatialfilters.
 17. The method of claim 15, wherein the angular separations ofthe expected components scattered by the pattern on the surface is notless than a value, and the gap and offset are substantially equal tosaid value.
 18. The method of claim 17, further comprising providingsignals in response to the filtered first and second portions of thecollected radiation, and combining the signals to detect anomalies in oron the surface.
 19. The method of claim 14, wherein said expectedcomponents scattered by the pattern are Fourier components.
 20. Asurface inspection apparatus for detecting anomalies on a surface,comprising: a source supplying a beam of radiation scanning the surface;a collector collecting radiation scattered from the surfacesubstantially symmetrically about a line normal to the surface; opticsincluding optical channels at different azimuthal angles about the lineor about a direction corresponding thereto, the collector supplying thecollected radiation to the channels so that information related torelative azimuthal positions of the collected radiation about the lineis preserved, and the channels are disposed so that radiation scatteredby the surface at different azimuthal angles with respect to the line isconveyed by different channels, said optics including separatorsseparating the channels from each other to reduce crosstalk; a pluralityof detectors converting the collected radiation carried by at least someof the channels into respective signals representative of radiationscattered at different azimuthal angles about the line; and a processordetermining the presence of anomalies in or on the surface from saidsignals.
 21. The apparatus of claim 20, said optics including opticalfibers, each of said fibers including a core and cladding, said claddingbeing the separators.
 22. The apparatus of claim 20, said channelsdisposed symmetrically about the line or the direction.
 23. Theapparatus of claim 20, said channels disposed at elevation angles awayfrom expected components scattered by the pattern.
 24. The apparatus ofclaim 23, wherein said expected components scattered by the pattern areFourier components.
 25. The apparatus of claim 20, wherein said channelsare substantially at elevation angles between about 5 and 9 degrees fromthe line or the direction.
 26. The apparatus of claim 20, wherein saidcollector including a lens or a curved mirrored surface.
 27. Theapparatus of claim 26, wherein said collector including an ellipsoidalor paraboloidal mirrored surface.
 28. The apparatus of claim 27, saidmirrored surface defining therein at least one aperture, said apparatusfurther including at least one multiunit detector detecting radiationfrom the surface through the aperture, and at least one spatial filterfiltering the radiation from the surface detected by the at least onedetector.
 29. The apparatus of claim 28, said at least one detectorincluding detecting units that are substantially rectangular in shape,said at least one filter including an array of stripes of opaquematerial.
 30. The apparatus of claim 28, further comprising a rotatablemember supporting the at least one filter, and a device causing themember to rotate.
 31. The apparatus of claim 30, said member definingtherein an S-polarizer.
 32. The apparatus of claim 31, said S-polarizersubstantially in the shape of a circle or semicircle.
 33. The apparatusof claim 30, said at least one filter including a striped spatial filterfiltering the radiation from the surface detected by the detectors sothat odd or even detecting units are shielded from scattered radiationfrom the surface through their corresponding apertures, said rotatablemember supporting the striped spatial filter.
 34. The apparatus of claim27, said mirrored surface defining therein two apertures facing eachother, said apparatus further including two multiunit detectors facingeach other, each detector detecting radiation from the surface through acorresponding aperture, and two masks, said detectors includingdetecting units that are substantially rectangular in shape, each of thetwo masks masking every other detecting units of a correspondingdetector, the two masks placed offset relative to each other by an oddnumber of detecting units.
 35. The apparatus of claim 34, said beambeing at an oblique angle to the surface, said two apertures beingsubstantially centered at + and −90 degrees azimuthal angles relative toa plane of incidence of the beam.
 36. The apparatus of claim 20, whereinsaid collector including a lens with an axis substantially along saidline or direction.
 37. The apparatus of claim 20, said optics furthercomprising means diverting a portion of the collected radiation to saidchannels, said apparatus further including a detector detecting anotherportion of the collected radiation to provide a single output.
 38. Theapparatus of claim 37, said diverting means including a mirror or a beamsplitter.
 39. A surface inspection apparatus for detecting anomalies ona surface having a diffracting pattern thereon that scatter radiation,said apparatus comprising: a source supplying a beam of radiationscanning the surface; a collector collecting radiation scattered fromthe surface substantially symmetrically about a line normal to thesurface; a spatial filter filtering at least a portion of the collectedradiation, said filter having an angular gap therein of an angle relatedto the angular separation of expected components scattered by thepattern on the surface; and a processor determining the presence ofanomalies in or on the surface from said filtered collected radiation.40. The apparatus of claim 39, said apparatus comprising a first and asecond spatial filter filtering respectively a first and a secondportion of the collected radiation, the two spatial filters each havingan angular gap therein, the gaps of the two filters being offsetrelative to each other by an angle with respect to the line and relatedto the angular separations of the expected components scattered by thepattern on the surface.
 41. The apparatus of claim 40, wherein theangular separations of the expected components scattered by the patternon the surface is not less than a value, and the gap and offset aresubstantially equal to said value.
 42. The apparatus of claim 41, theprocessor providing signals in response to the filtered first and secondportions of the collected radiation, and combining the signals to detectanomalies in or on the surface.
 43. The apparatus of claim 40, furthercomprising a divider dividing the collected radiation into the first andsecond portions that are filtered by the two spatial filters.
 44. Theapparatus of claim 39, wherein said expected components scattered by thepattern are Fourier components.
 45. A surface inspection method fordetecting anomalies on a surface, wherein a beam of radiation isprovided to scan the surface, employing an apparatus comprising a firstnear normal collection system collecting and directing radiationscattered by an area of the surface along directions near a lineperpendicular to the surface to a first detector, a second collectionsystem including a curved mirrored surface having an axis of symmetryabout said line reflecting and directing radiation scattered from thearea of the surface along directions away from said line to a seconddetector; said method comprising: obtaining from the first detector afirst output signal in response to scattered radiation from the beam andthe area of the surface; obtaining from the second detector a secondoutput signal in response to scattered radiation from the beam and thearea of the surface; and deriving a ratio of the first and second outputsignals to determine whether an anomaly on the surface is amicro-scratch or a particle.
 46. The method of claim 45, furthercomprising providing the beam in an oblique direction to the surface,wherein the anomaly is determined to be a particle where the ratio isclose to 1, and to be a micro-scratch where the ratio is less than apredetermined fraction.
 47. The method of claim 46, wherein saidfraction is about 0.8.
 48. The method of claim 45, further comprisingproviding the beam in a oblique direction to the surface, wherein theanomaly is determined to be a particle where the first output signal isnonzero and the second output signal is substantially zero, and to be amicro-scratch where the first output signal is substantially zero andthe second output signal is nonzero.
 49. The method of claim 45, furthercomprising providing the beam in a direction substantially normal to thesurface, wherein the anomaly is determined to be a particle where theratio is close to 1, and to be a micro-scratch where the ratio is largerthan a predetermined quantity greater than
 1. 50. The method of claim49, wherein said quantity is about 1.6.
 51. The method of claim 45,further comprising providing the beam in a direction substantiallynormal to the surface, wherein the anomaly is determined to be amicro-scratch where the first output signal is nonzero and the secondoutput signal is substantially zero, and to be a particle where thefirst output signal is substantially zero and the second output signalis nonzero.
 52. A surface inspection method for detecting anomalies on asurface, employing a curved mirrored surface having an axis of symmetryabout said line reflecting and directing radiation scattered from thearea of the surface along directions away from said line to a seconddetector; said method comprising: providing a beam of radiation in anoblique direction to the surface to scan the surface; separatelycollecting radiation scattered by the surface along forward scatteringdirections from other scattering directions and detecting separately theseparately collected radiation to provide a first signal indicative ofthe collected forward scattered radiation and a second signal indicativeof the collected scattered radiation other than forward scatteredradiation; comparing the two signals to determine whether an anomaly onthe surface is a micro-scratch or particle.
 53. The method of claim 52,wherein said comparing includes comparing the ratio of the two signalsto 1, and calling the anomaly a particle where the ratio is close to 1and a micro-scratch where the ratio of the first signal to the secondsignal is greater than a predetermined quantity.
 54. The method of claim52, wherein said comparing includes calling the anomaly a micro-scratchwhere the first signal is nonzero and the second signal is substantiallyzero, and otherwise calling the anomaly a particle.
 55. The method ofclaim 52, wherein said separate collection is performed by directing thescattered radiation along separate optical channels separated from eachother by separators.
 56. The method of claim 52, wherein said separatecollection is performed by directing the scattered radiation throughspatial filters in the shape of masks with the forward scatteringdirections blocked, or blocking all scattering directions except for theforward scattering directions.
 57. A surface inspection method fordetecting anomalies on a surface, employing a curved mirrored surfacehaving an axis of symmetry about said line reflecting and directingradiation scattered from an area of the surface along directions awayfrom said line to a second detector; said method comprising: providingsequentially a radiation beam of a first state of polarization and abeam of a second state of polarization at oblique direction(s) to thesurface to scan the surface, said first and second states beingdifferent; collecting radiation scattered by a defect during thesequential scans and providing a pair of signals: a first comprising asignal indicative of the collected scattered radiation when the surfaceis scanned by radiation in the first state of polarization and a secondcomprising a signal indicative of the collected scattered radiation whenthe surface is scanned by radiation in the second state of polarization;and comparing the two signals to determine whether an anomaly on thesurface is a micro-scratch or particle.
 58. The method of claim 57,wherein said comparing includes deriving a ratio of the signals toobtain a ratio, and comparing the ratio to a predetermined referencevalue.
 59. The method of claim 57, wherein said first and second statesof polarization are the S-polarization and P-polarization states.
 60. Amethod for determining roughness of a surface, comprising: providing adatabase correlating haze values with surface roughness of thin films;measuring haze values of the surface; and determining a roughness valueof the surface from the haze value and the database.
 61. The method ofclaim 60, said providing including: measuring haze values of thesurfaces of representative thin films; and measuring roughness values ofsaid surfaces; and compiling said database.
 62. The method of claim 61,wherein said roughness values measuring is performed by means of aprofilometer or a scanning probe microscope.